Frequency control for a multiplex distributing system



Jan. 15, 1935. H. P. CORWITH ET AL FREQUENCY CONTROL FGR A MULTIPLEX DISTRIBUTING. SYSTEM 1932 I5 SheetsSheet 1 Filed June 9 M R H D Y OTNRU MMWKN 5mm MM WCH T P H 1 H H rGA Jan. 15, 1935. H. P. CORWITH ET AL FREQUENCY CONTROL FOR A MULTIPLEX DISTRIBUTING SYSTEM Filed June 9, 1932 5 Sheets-Sheet 2 mm W 0 We NP 1.

H. H, HAGLUND Jan. 15, 1935. H. P. CORWITH El AL FREQUENCY CONTROL FOR A MULTIPLEX DISTRIBUTING SYSTEM Fiiled June 9, 1952 :5 Sheets-Sheet 3 FIG. 3

I IIIII Hi i CORRECTING RING LOCAL RING RECEIVING RING INVENTOR H. P. CORWITH H. H. HAGLUND Patented Jan. 15, 1935 v UNITED STATES PATENT OFFICE FREQUENCY CONTROL FOR A MULTIPLEX DISTRIBUTING SYSTEM Application June 9, 1932, Serial No. 816,834

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This invention relates to a multiplex telegraph system and more particularly to the maintenance of synchronism between the individual circuits of such a system.

In present day multiplex systems, it is the practice to provide an individual driving fork for the motor of each multiplex distributor, each fork being adjusted to the frequency of the circuit as sociated with its distributor. The distributors at the opposite ends of a circuit, of course, operate at substantially the same frequency, small variations in speed of the two distributor motors being compensated by the correcting mechanism associated with one distributor. The frequency of the forks is not absolutely constant, however, but varies from minute to minute and from hour to hour, depending upon temperature changes, current variations and other variables. .Such forks can be maintained at very constant frequencies, however, if sufficient precautions are taken but the equipment, maintenance and supervision required to insure such accuracy render it impractical to do so and consequently no two circuits operate at exactly-the same frequency. Theretherefore, to provide a means whereby a large number of multiplex circuits, associated with a number of widely separated ofllces, may be operated at a uniform frequency or at a frequency which bears some definite and fixed relation to such uniform frequency.

Another object is to maintain a standard frequency control for a plurality of stations having interrelated multiplex circuits, whereby channels of one circuit may be operated over the channels of another circuit.

A further object is to provide an improved driving arrangement for phonic motors.

A still further object isto produce an arrangement whereby a large number of multiplex distributors may be operated accurately at different predetermined speeds,'each of which is in definite relation to a standard speed.

Other objects and advantages of the invention will appear as the description proceeds.

In accordance with one phase of our invention weestablishasinglestandardfrequencymrce at each station and control all of the multiple:

distributor motors at the station from such source of standard frequency. The individual motors may operate at the same frequency as the source or at a different frequency. By thus providing only a single source of frequency for all distributors this source may be of a more expensive and more constant type than the usual individual fork control. For instance, it may be a piezo electric crystal controlled oscillator, a magneto striction controlled oscillator or a vacuum tube driven tuning fork. By way of example the latter type will be shown in detail hereinafter.

It is, of course, necessary to subdivide the frequency produced by this standard source since all distributors do not operate at the same speed. The subdivision may be eflected by any one of several known types, as for instance, multivibrators or oscillators controlled by harmonics or subharmonics of the standard frequency but preferably we drive a motor from the standard frequency source which in turn controls the operation of several commutators having different numbers of pairs of segments and cooperating brushes whereby a direct current source may be opened and closed or reversed in polarity to furnish the desired frequencies for driving the motors of the multiplex distributors.

It is not desirable, however, to drive the motor directly from such commutator device since a considerable amount of power would have to be taken from the commutators. Particularly where a number of distributors are driven at the same speed. This in turn causes serious arcing at the brushes and necessitates the use of large size leads to connect the commutators with the motors. We prefer, therefore, to use a current obtained from the commutators only as a control source so that only a small amount of current is required.

This is accomplished in the embodiment described in detail' hereinafter by using an inverter employing electro-statically controlled are discharge tubes for supplying drive current to the distributor motors, the frequency supplied by the commutators serving only for controlling the ds of the tubes.

If the commutators are arranged so as to furnish a given oillce with a number of different frequencies all accurately maintained, all of the distributor motors at that station may be driven at any speed corresponding to one of the frequencies so supplied, the number of available speed steps being dependent upon the number of supplying the various control frequmcies. Since imder proper conditions the standard source of frequency can be made accurate at least to one part in a hundred thousand or better, a distributor that is designed to operate at a definite speed will actually run at such speed with an error of less than one part of a hundred thousand. This speed control is suiliciently close to permit an ofiice so equipped to connect the channels of a distributor running at one speed,

to the channels of another distributor running at the same speed, by means of channel repeaters or similar devices without danger of the receiving side gaining on the sending side. A very flexible system is, therefore, produced in which channels may be interrelated conveniently.

The invention will be best understood by the following detailed description of a preferred embodiment thereof, in connection with the accompanying drawings and the scope of the invention can be ascertained from the appended claims.

Referring to the drawings, Figure 1 shows, diagrammatically, a portion of a multiplex system embodying our invention, and Figures 2 and 3 taken together show the detail circuit diagrams of the operating parts of the system.

Referring first to Figure 1, we have shown a portion of the equipment at two stations A and B. At each station there is provided a source of standard frequency F which is accurately maintained and which serves through an amplifier A to operate a motor M, which may be of a phonic type, for driving a group of commutators C1, C2, C3 etc. Each of the commutators has a definite number of segments and cooperating brushes whereby as the commutators revolve different frequencies will be set up in the control conductors 1, 2, 3,, 4, 5, etc.

At station A the commutator C1 serves to control multiplex distributors D1 and D2, each of which has a receiving face plate RD and a transmitting face plate TD. Each of the sets of distributors D1 and D2 has an individual driving unit represented by the enclosures DUI and DU2 and including an inverter employing electrostatically controlled arc discharge tubes. The details of this motor driving unit will appear more fully hereinafter. Similarly the commutator C2 controls a group of distributors D3, D4 and D5. The commutators C3 likewise controls the pairs of distributors D6 and D7 and commutators C4 and C5, etc. may control any desired number of additional pairs of distributors.

The speed of each distributor depends, of

course, upon the frequency supplied by its associated commutator, for instance, if the standard frequency is assumed to be 50 cycles per second, certain of the commutators may supply frequencies below this value and others may supply frequencies above this value. As a typical assignment the commutator C1 may produce a frequency of 40 cycles; C2, 45 cycles; C3, 50 cycles; C4,

55 cycles; etc., by equal steps to a hundred ormore cycles.

Each of the circuits associated with a particular distributor is shown duplexed although this is not essential- For instance, distributors D2 and D5 are associated with the lines L2 and L5 respectively extending between the stations A-and B. A repeater R may be provided in each line.

if necessary. The remaining distributors may be associated with circuits extending to other stations, in any desired arrangement. For instance distributors D1 and D3 are provided for the lines L1, L3 extending to station C and distributors D4 and D6 are associated with lines L4, L6 extending to station D. Distributor D7 is shown connected to line L7 terminating at station E. I

It will be understood that at the opposite terminal each circuit is provided with a distributor operating at, the same speed as those at station A. For instance, lines L2 and L5 terminate at distributors D2 and D5 at station B controlled by the commutators C1 and C2 whichprovide the same frequency as the correspondingly numbered commutators at station A. v

'In connection with distributors D6 and D7 at station A, we have shown channels of one of the associated circuits working into channels of the other circuit. For instance, the signals received over three channels of the circuit L6 are distributed to multiplex printers through the receiving face plate RD of distributors D6, and the conductors 10. The signals received over the fourth channel are repeated through a channel repeater CR, to one channel of the transmitting face plate TR of the distributors D7, for transmission over the line L7. Likewise signals received over two channels of the circuit L7 are repeated through channel repeaters CR2 and tion may be similarly associated with the channels of other circuits terminating at the same station as long as the circuits are operating at the a same speeds.

Reference will now be had to Figures 2 and 3 showing in detail, circuit diagrams of .the essential'features of the preferred embodiment of the invention. The standard source of frequency is illustrated as a vacuum tube controlled tuning fork 20 which may be contained within a double walled receptacle 21 having heating coils 22 disposed between the chambers for maintaining a constant temperature condition within the chamber. The temperature is accurately controlled by means of a thermostat 23 which regulates the heating currents supplied to the coils 22.

The circuit for the heating elements 22 includes resistors 24 and 25, the latter of which is adapted to be short-circuited through the front contact of a temperature control relay 26. As shown, the relay 26 is energized from asuitable source of current so as to short circuit the resistor 25 and thereby supply the maximum heating current to the heating elements. As the temperature in the chamber increases, the mercury within the thermostat 23 rises until it bridges the contacts 27 and 28, short-circuiting the winding of the relay 26 and allowing its contacts to open thereby inserting the resistor 25 in the heating circuit and consequently reducing the heating current. As the temperature of the chamber again decreases, it will be understood of course that relay 26 again picks up, cutting out the resistance 25. The temperature, therefore, is maintained very closely to the level corresponding to the contact 28.

A signal 29 is provided, however, to indicate to the attendant should the temperature of the fork chamber increase or decrease a substantial amount from this desired value. The signal is controlled by a relay 31 which normally holds the signal circuit open, the relay circuit being traced from positive battery through the conductor 32, relay 31, thermometer contacts 33 and 27 to negative battery. If for any reason the temperature should rise to the level indicated by the contact 34, the relay 31 would be short-circuited across contacts 33 and 34, allowing the relay tongue to fall back and complete the signal circuit. On the other hand should the temperature decrease to a point below that indicated by the level of the contact 2'7, the circuit to the relay 31 would be interrupted at this contact, causing the signal to operate. The attendant is thereby informed that the required temperature control is not being maintained and may, by manipulation of the resistances 24 or 25 or otherwise restore the proper control.-

The fork 20 is provided with driving magnets 36, damping magnets 3'7 and pick up coils 38. The driving magnets 36 are in circuit with the secondary of a transformer 39, the primary of which is included in the output circuit of a vacuum tube 41. I

In order that the voltage for the output circuit of the tube 41 may be maintained constant regardless of line variations, we prefer to employ rectified current from an alternating current source, the voltage of which may be more readily controlled. To this end the current from an alternating current source 42 is passed through a voltage regulator 43 of any approved tube, shown herein as including a compensating transformer and the regulated current is rectified by means of the full wave vacuum tube rectifier 44, the irregularities being eliminated bymeans of an appropriate filter circuit 45-.

The output circuit of the tube 41 is completed from the positive terminal of the rectifyingsystem through the primary of the transformer 39 to the anode of the tube and thence from the cathode through the midpoint of the secondary winding of the heating transformer 46 and biasing battery C1 to the negative terminal of the rectifier. The tube is modulated in accordance with the natural frequency of the fork by means of the pick-up coils 38, the vibration of the fork tines to and from the cores of the pick-up coils producing a change in the fiux threading the coils to generate an oscillating voltage which is impressed upon the grid of the tube 41 by a circuit completed from the grid through the coils 38 in series and thence to the cathode through battery C1. The circuit for the damping coils 37 is completed directly from the positive terminal of the rectifier through the coils 37 in series andthence through the variable resistance 47 to the negative terminal of the rectifier.

It will be appreciated that after the fork has been set into vibration by any manual means the tube 41 will continue the supply driving current therefor, of a frequency corresponding to the natural frequency of the fork. As previously stated, under properly controlled conditions this frequency can be accurately maintained at least within one part in a hundred thousand.

The constant source of frequency thus generated in the pick-up coils 38 is employed to drive an electric motor 51 which we have illustrated as of the phonic type. is the group of commutators C1, C2, C3, etc. While we have shown but four commutators it is to be understood that if it is desired twenty or more of such commutators may be provided. The commutators each have a different number of segments and are each provided with a pair of brushes52, 53. The opposite contacts of the commutators are connected through slip rings (not shown) with battery of opposite polarity so that as they revolve an alternating current is produced between the brushes 52 and 53, the fre- On the shaft of this motor' quency of which depends upon the number of segments in each commutator. In this manner any desired number of frequencies can be obtained having a definite relation to the frequency of the fork 20 and varying therefrom in definite steps. For instance, if the frequency of the fork is assumed to be 50 cycles per second .the frequency derived from the commutator may readily be varied from 40 cycles or less to cycles or more by steps of 5 cycles.

Due to the large number of commutators which it is desired to operate from a single motor, a current of considerable magnitude is required to drive the motor 51 and this current must be of symmetrical form in order to eliminate irregular operation thereof. The current induced in the pick-up coils 38 is of a very low magnitude and due to extraneous flux set up by the driving coils 36 in the tines of the fork, the current induced. in the coils 38 is not entirely symmetrical. Therefore, we have provided an amplifying and wave shaping arrangement intermediate the pick-up coils and the motor 51. This comprises a pickup tube 55, a wave filter 56, amplifying tubes 5%" and 58 arranged in push-pull relation and an. inverter employing tubes 59, 61 of thegrid controlled arc discharge type.

The input circuit of the pick-up tube 55 also includes the pickup coils 38, so that this tube is modulated in accordance with the current induced therein in the same manner as the tube 41. In order that the voltage regulating and rectifying system may be kept at a low output and, therefore, more readily regulated, we prefer to employ a separate source 62 of current for the output circuits of the tubes 55 to 61. The anode andcathode of the tube 55 are connected directly across this source of current 62 through. the primary of a transformer 63 by which the output circuit of the tube 55 is coupled to a wave filter 56. The elements of filter 56 are so adjusted as to eliminate the undesirable harmonics in the generative wave and thereby to restore the same substantially to sinusoidal form. The shaped alternating current is then passed through the primary winding of a transformer 64, the secondary of which is included in the input circuits of the push-pull amplifying tubes 57, 58, this amplifier being of conventional form. The amplified current is then applied to the input circuits of the arc discharge tubes 59 and 61. The anode of the tube 61 is connected by a conductor 65 to the oppositely disposed coils' 66, 67 of the phonic motor 51, and thence through the differential meter 68 to the positive side of the current supply 62. The anode of the tube 59 is similarly connected through the coils 69, '11 of the motor. The cathodes of the tubes 59 and 61 are connected to the negative side of the supply conductor and to the midpoint of the coupling transformer 72. A condenser 73 is provided direction as to render the grid of the tube 59 more positive and that 'of the tube 61 less positive,a discharge will be started through the tube 59 the output circuit extending from the nega- Assuming current to be flowing through tive.

tive side of the supply line 62, to the cathode of tube 59, thence to the anode thereof and through coils 66 and 67 of the motor back to the positive supply conductor. This discharge will continue until a reversal of current occurs in the transformer 72 such as will render the grid of the tube 61 more positive and that of tube 59 less posi- The variation of potential of the grid of the tube 59 does not affect its operation but. the

rendering of the grid of the tube 61 more positivestarts a discharge therethrough energizing the coils 69 and 71 of the motor. At the time this discharge starts there is a reversal of the charge on the condenser 78 which is in a direction counter to the discharge through the tube 59 thereby momentarily reducing the plate current in this latter tube to such an extent that the discharge is extinguished. The tube 61 continues to operate until another reversal occurs starting the tube 59 again into operation. In this manner the tubes 59 and 81 operate alternately and in phase with the applied current, supplying the operating current for the phonic motor.

We have shown an ordinary synchronously driven clock 74 connected between the anodes of the tubes 59 and 61 so as to be controlled thereby. If the frequency of the standard source is 60 cycles a standard electric clock may be employed. If a diiferent standard frequency is employed it will be necessary to change the gear ratio of the clock accordingly. This clock is used purely for check purposes and may be compared from time to time with a standard source of time such as a chronometer or observatory transmitted signals. The condenser 75 is included in circuit with the clock.

it will be apparent from the foregoing that we have provided a source of frequency which may be very accurately maintained and which is of sufiicient amplitude to operate a comparatively powerful motor. The use of a large number of commutators in addition to supplying the required frequencies serve by their flywheel effect to maintain the motor at a constant speed so that any variation which may occur in the driving current is absorbed and uniform operation of the motor obtained. It will be understood that each of the commutators supplies current for operating one or more distributors and we'have shown in Figure 3 a typical circuit diagram of a single distributor controlled by one of the commutators C4. v

The distributor shown in Figure 3 comprises the transmitting face plate TD driven by a phonic motor 81 and a receiving distributor RD driven by a phonic motor 82. Each of the motors 81 and 82 is provided with an inverter employing gaseous conduction devices similar to that used to drive the phonic motor 51. Considering the inverter associated with tube 81, it will be noted that the brush 52 of the commutator C4 is connected those of tubes 84 and 85 to controlthe operation of the motor 82.

The transmitting face plate TD is of conventional design two channels thereof only being 'constantfrequency for controlling the rate shown. Signals set up by the transmitters T1 and T2 are applied to the contacts of the transmitting ring 88 and transmitted by means of the brush 88 and solid ring 91 to the apex of the duplex set 92 and thence over the line L. The usual perforated tape is stepped through the transmitters T1 and T2 by the stepping magnets SMi and M2 controlled by appropriatesegments of local rings 98 and 94.

The receiving distributor RD comprises a pair of receiving rings 95 and 96, local rings 97 and 98 and correcting rings- 89 and 100. The tongue 101 of the receiving relay is connected by conductor 102 to the winding of local relay 103 which repeats the incoming signals over conductor 104 to the solid receiving ring 196 and thence through the segmented ring 95 to the selecting magnets 105 of the receiving multiplex printers 106 and 107. The printing stroke for each printer is completed by the printing magnets 108 and 109, respectively, controlled through appropriate segments of the local rings9'l and 98 over conductors 110 and 111.

The proper phase relation between the transmitting distributor at the opposite end of the duplex line L and the receiving distributor RD is maintained by a correcting mechanism, which is shown as of the type disclosed in a copending application of O. E. Pierson, Serial No. 537,732, filed May 15, 1931 and entitled Correcting mechanism for synchronous apparatus. This correcting scheme forms no part of the present invention and therefore is not described in detail. It is sufficient to say that whenever an out of phase condition occurs a correcting relay 112 controlled jointly by the correcting rings 99 and 100 and a rectifying bridge 113, supplies operating current to a motor 114 mounted on the distributor shaft to rotate therewith. The operation of the motor 114 in either direction advances or retards the distributor face plate through appropriate gearing 115 and 116 so as to restore the phase rela tionship.

While a specific embodiment of the invention has been shown it is to be understood that it may take various other forms and therefore we do not desire to be limited to the exact details shown and described but contemplate all variations coming within the scope of the appended claims.

What we claim is:

1. Incombination, a multiplex circuit, a distributor therefor, a phonic motor for driving said distributor and an inverter comprising alternately operating gaseous conduction tubes for supplying current of a definite frequency for operating said motor.

2. In a telegraph system, a distributor for system, a signaling circuit associated with said distributor, a phonic motor for driving said distributor, an'invertor comprising alternately op- 'erating gaseous conduction tubes for supplying operating impulses to said motor and a source of of alternate operation of said tubes.

3. In a telegraph system, a distributor for said system, a signaling circuit associated with said said distributor, a plurality of gaseous conduction tubes, output circuits for said tubes, 5. synchronous motor for driving said distributor, said motor havingseparate field windings in the output 4. In a telegraph system, a distributor fortributors for said system, signaling circuits associated with said distributors, a common source of frequency for controlling the rate of operation of said distributors, a plurality of gaseous-conduction tubes, output circuits for said tubes,'a synchronous motor for controlling said source of frequency, said motor having separate field windings in the output circuit of each tube, an input circuit for each tube, a sourceof electrical oscillations associated with said input circuits for producing discharges through said tubes alternately and a wave shaping network intermediate said source of oscillations and said input circuits.

6. In a telegraph system, a source of constant frequency, a phonic motor adapted to be operated from said source, a plurality of commutators driven by said motor, individual circuits for said commutators, a source of current connected to each commutator whereby as the commutators revolve oscillating currents of definite frequency will be applied to each of said circuits, a distributor corresponding to each circuit, a driving motor for each distributor connected in one of said circuits and signaling circuits associated with said distributors.

7. In a telegraph system, a source of constant frequency, a phonic motor adapted to be operated from said source, a plurality of commutators driven by said motor, the number of segments on said commutators being non-uniform, individual circuits for each commutator, a source of current connected to each commutator whereby as the commutator revolves oscillating currents of different frequencies will be applied to said circuits, a distributor corresponding to each circuit, a driving motor for each distributor connected in one of said circuits and signaling circuits associated with said distributors. v

8. In a telegraph system, a plurality of distributors for said system, signalling circuits associated with said distributors, a common source of frequency for controlling the rate of operation of said distributors, a synchronous motor for controlling said source of frequency, a plurality of gaseous conduction paths having output circuits associated with said motor for driving the same by current supplied through said paths, controlling circuits. for said discharge paths, a vibratory fork having a natural period of vibration, means associated with said fork for producing electrical oscillations having a frequency proportional to the frequency of the fork, a wave shaping network for modifying the wave form of said oscillations and means for impressing said oscillations on said controlling circuits whereby to produce current flow in said output circuits alternately to operate said motor.

HOWARD P. CORWITH. HAKON H. HAGLUND. 

